[Cosmic_announce] timestamps in ionPrf file names

[Stig Syndergaard]

Dear data users,

Important note on time stamps in ionPrf file names downloaded from 
CDAAC and TACC:

ionPrf files processed before 9/27/2006: 
The time in the ionPrf file names represents the time when the tangent 
height of the LEO-GPS link is at an altitude of about 150 km.

ionPrf files processed since 9/27/2006: 
The time in the ionPrf file names represents the stop time of the data 
used in the processing for a given occultation. For setting occultations 
this is usually when the tangent height of the LEO-GPS link is near 
the Earth's surface. This would be a few to several minutes after the 
occultation rays probed the bulk of the ionosphere. For rising occultations, 
the time in the file names may be a few tens of minutes after the 
occultation rays probed the bulk of the ionosphere. This is because 
we are using data collected at positive elevation angles in the processing 
when such data are available. Thus, the timestamps in the ionPrf file names
since 9/27/2006 may not be that representative of the time of ionospheric 
occultation. Currently, the indication of whether an occultation is 
rising or setting can only be found in the corresponding ionPhs NetCDF files. 

We apologize for any inconvenience this may cause, and we are working on 
solutions to make the times in the file names more consistent with the 
times of the occultations.

Regards
-Stig Syndergaard 

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Stig Syndergaard, PhD 
UCAR COSMIC Project Office                   Phone: (303) 497 2614
P.O. Box 3000                                  Fax: (303) 497 2610
Boulder, CO 80307-3000                        E-mail: ssy at ucar.edu
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